There's a more thorough version of this at https://www.youtube.com/watch?v=RSaJAAqSAMw and the end-result doesn't look as tacky
if you want to do this, there is a better technique than shown in this video.
get a single-cut fine file, maybe with a little more weight than the one in the video. single cut file has diagonal slots and allows firm and continuous contact with the piece. most files are double cut, have two sets of slots and look like bumpy diamonds. they remove more material but tend to bounce.
use long even strokes with firm pressure, only during the fore stroke. watch out for roll-off, where you unconsciously change the angle or pressure of the file as you're at the end of the stroke.
you can make a pretty even-looking chamfer that way.